Printed circuit boards are well known and are widely used in forming complex circuits. A circuit board, to which other electrical components may be joined, includes conductive tracks formed on the surface of the board by copper coating and may also include holes extending through the board. The surfaces of the holes may also be copper coated such that components which are joined to the circuit board at the holes form an electrical connection with the copper coating on the hole surfaces. Circuit boards may, also, have conductive tracks formed on both the top and the bottom surface of the board with conductive holes passing through the board forming an electrical connection between the tracks on the top and the bottom surfaces.
After forming a circuit board through any procedure, it is desirable to protect the copper coating on the board from oxidation. One convenient means of protecting the copper coating is to coat the copper coating with solder. In addition to protecting the copper coating on the board, the solder provides for the connection of electrical components with the circuits defined by the copper coating on the surfaces of the board.
At present, there is no satisfactory procedure or apparatus for continuously applying a solder coating to the copper-coated surfaces of the circuit board. In machines which are presently in use, boards are sequentially moved from one work station to another in performing the steps required to form a solder coating on the copper-coated surfaces of the circuit board. While such machines may operate at a relatively high rate of speed, their operation cannot be termed continuous because there is a dwell time at each station where a work operation is carried out on the circuit board.
In coating a circuit board with solder, the board may be dipped into a molten bath of solder. This procedure is unsatisfactory because different portions of the circuit board which are to be coated with solder are not exposed to the solder bath for equal periods of time. Thus, the solder coating on the various portions of the board may be nonuniform. To illustrate, the portion of the circuit board which is first immersed in the molten solder will be the last portion to be removed from the molten solder. Conversely, the last portion of the circuit board to enter the molten solder bath will be the first portion of the board to be removed.
In view of the above-described problems, it would be desirable if a process and apparatus could be devised for continuously coating circuit boards with solder. Circuit boards could then be coated with solder without the loss of time which occurs at the various work stations in a batch-type operation. Also, it would be desirable if a process and apparatus could be devised in which circuit boards are more uniformly coated with solder. The various portions of the circuit board would then be exposed to molten solder for approximately equal periods of time. This would be an improvement over procedures in which a circuit board is dipped into a bath of molten solder with various portions of the circuit board being exposed to the molten solder for unequal periods of time.